Plate 29.
HIGH BALL CUMULUS.
(Alto-cumulus Glomeratus.)
Plate 29.
HIGH BALL CUMULUS.
(Alto-cumulus Glomeratus.)
If it were possible to take a good typical example of the variety just described and roll it flat, so that each cloudlet should be reduced to a lenticular shape, we get a type which seems seldom to appear during the heat of the day, and to be most frequent about sundown. It consists, as shown in Plate [30], of distinct cloudlets, with considerable spaces between them, and gives the impression of a discontinuous level sheet. But the component cloudlets are much too definite, and preserve their individuality far too well to suggest any idea of a broken stratus; the spotted structure is the predominant feature, while the stratiform arrangement is almost equally plain. Alto-stratus maculosus would be a suitable term. It is not so high a cloud as the glomeratus type, the one shown being at an altitude of about 5600 metres. The plate shows the position of the setting sun, which is partly hidden behind some dark patches of broken alto-stratus (fracto-alto-stratus), the hazy form and boundaries of which form an effective contrast to the shining cloudlets 2000 metres or so above them. Many of our most beautiful sunsets are due to this form of cloud, particularly in the late autumn. It is a cloud of calm weather, and often floats apparently motionless, and undergoing little change, like flakes of glowing fire against the background of a fading sky long after the sun has disappeared. It is not indicative of thunder conditions, and it may occur on the margins of an anticyclone.